WASHINGTON -LRB- CNN -RRB- -- President Bush on Tuesday announced a troop deployment shift for America 's two wars , a move that reflects a more stable Iraq and an increasingly volatile Afghanistan .

President Bush said Tuesday that he soon will start bringing some U.S. troops home from Iraq .

Through early next year , about 8,000 American troops will leave Iraq and not be replaced . Some 4,500 other U.S. service members will go to Afghanistan .

Bush also emphasized the U.S. intention to help Pakistan defeat insurgents who are using the country 's tribal areas to stage attacks in Afghanistan .

`` Iraq , Afghanistan and parts of Pakistan pose unique challenges for our country , '' Bush said Tuesday in a speech at the National Defense University in Washington . `` Yet they are all theaters in the same overall struggle . ''

Bush said he is making the Iraqi troop withdrawal decision based on a recommendation from top military officers , including Gen. David Petraeus , the highest-ranking U.S. military officer in Iraq . Watch Bush announce the troop reduction in Iraq ''

`` He and the Joint Chiefs of Staff have recommended that we move forward with additional force reductions , '' the president said , citing military and political strides in stabilizing the country and dramatically bringing down violence .

Bush adopted the entire recommendation from Petraeus , a senior military official in Iraq told CNN . The source said five people saw the plan before it went to the president . Debate the Iraq issue ! Join The Forum

In explaining progress in the war effort , Bush cited the `` surge '' offensive , winning the hearts and minds of Sunni tribes , Iraqi political reconciliation efforts , economic improvements , an improved Iraqi army leading the fight against Shiite and Sunni insurgents , and a return of hundreds of doctors who fled the fighting .

`` Over the next several months , we will bring home about 3,400 combat support forces -- including aviation personnel , explosive ordnance teams , combat and construction engineers , military police and logistical support forces , '' he said . `` By November , we will bring home a Marine battalion that is now serving in Anbar province . And in February of 2009 , another Army combat brigade will come home .

`` This amounts to about 8,000 additional American troops returning home without replacement . And if the progress in Iraq continues to hold , Gen. Petraeus and our military leaders believe additional reductions will be possible in the first half of 2009 . ''

At present , there are about 146,000 U.S. troops in Iraq .

An adviser to Iraqi Prime Minister Nuri al-Maliki welcomed Bush 's decision .

`` We look at this step as a positive step that there is stability in Iraq , there is a real improvement in the security situation in Iraq and there is a real improvement in the capability of the Iraqi security forces in protecting and keeping the security in Iraq , '' said Sadiq al-Rikabi , al-Maliki 's political adviser .

Democrats were less than enthusiastic about Bush 's announcement .

The plan `` may seem to signal movement in the right direction , '' but it `` defers troop reductions until the next administration , '' said Rep. Ike Skelton , D-Missouri , chairman of the House Armed Services Committee .

`` More significant troop reductions in Iraq are needed so that we can start to rebuild U.S. military readiness and provide the additional forces needed to finish the fight in Afghanistan . ''

Skelton said Iraq `` can not continue to overshadow other critical U.S. security needs . ''

`` The effort in Afghanistan must move to the forefront and once again become our top priority , '' he said .

Democratic presidential nominee Sen. Barack Obama praised Bush for announcing additional troops for Afghanistan and `` moving in the direction of the policy that I have advocated for years . ''

However , `` we will continue to spend $ 10 billion a month in Iraq while the Iraqi government sits on a $ 79 billion surplus , '' Obama said .

`` In the absence of a timetable to remove our combat brigades , we will continue to give Iraq 's leaders a blank check instead of pressing them to reconcile their differences , '' he said .

Obama criticized the timing and scope of Bush 's move .

`` His plan comes up short -- it is not enough troops , and not enough resources , with not enough urgency , '' the senator from Illinois said of Bush 's call for more troops in Afghanistan .

In his speech , Bush praised other members of the U.S.-led coalition , saying many of those nations will be able to end their deployments to Iraq this year . He said Australia has `` withdrawn its battle group '' and Polish troops are `` set to redeploy shortly . ''

The president said Iraq and the United States will work `` toward the conclusion of a strategic framework agreement and a status of forces agreement , '' pacts that will spell out the terms of their relationship .

`` These agreements will serve as the foundation for America 's continued security support to Iraq once the United Nations resolution authorizing the multinational forces there expires on December 31 . ''

Bush focused his remarks just as strongly on Afghanistan , where al Qaeda and Taliban militants have been making a comeback .

`` For all the good work we have done in that country , it is clear we must do even more , '' he said . `` As we learned in Iraq , the best way to restore the confidence of the people is to restore basic security -- and that requires more troops . ''

He said that a Marine battalion of around 1,000 will deploy to Afghanistan in November instead of Iraq and that an Army combat brigade of around 3,500 will go in January .

Bush said the U.S. would make additional forces available in 2009 and called on allies to increase their force levels .

Bush said stepped-up insurgent efforts in Afghanistan have necessitated the increase of U.S. troops from `` less than 21,000 two years ago to nearly 31,000 today . ''

He said these troop increases and those by allies , including Britain , France , Poland , Bulgaria , Romania , Australia , Germany , Denmark and the Czech Republic , have resulted in what he calls a `` quiet surge '' in Afghanistan .

Bush described challenges in Afghanistan that do n't exist in Iraq .

`` This is a vast country , '' he said . `` Unlike Iraq , it has few natural resources and has an underdeveloped infrastructure . Its democratic institutions are fragile . And its enemies are some of the most hardened terrorists and extremists in the world . ''

He said Americans will help develop Afghan security forces and are improving efforts on the civilian side , adding more personnel to deal with issues of diplomacy , development , the rural economy and the fight against the drug trade .

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NEW : Sen. Barack Obama , House Armed Services chairman criticize scope , timing

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NEW : Iraq views decision as `` positive move , '' aide to Iraqi leader says

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Iraq force to be trimmed by 8,000 ; Afghanistan force to rise by 4,500

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President Bush cites increased stability in Iraq , stronger insurgency in Afghanistan